1. Field of the Invention
The present invention relates to a semiconductor memory device. More particularly, the invention relates to a semiconductor memory device having resistive elements providing improving memory cell density.
2. Description of the Related Art
Resistive Random Access Memory (hereinafter, ‘RRAM’) stores data by varying the resistance of a resistive element. Data may be written to a selected memory cell in an RRAM by applying a predetermined current to the corresponding resistive element. The amount of applied current may be controlled by defining a voltage potential difference between a bit line and a source line associated with the selected memory cell. RRAM generally includes types of RRAM in which different data values may be written in accordance with the polarity (i.e., the directional flow) of the applied current through the resistive element. Such devices are sometimes referred to as a “bipolar RRAM.” In the case of a bipolar RRAM, a bit line and source line are required for each memory cell in order to write different data values to the bipolar RRAM. As a result of this requirement, the size of a memory cell array becomes large.